Residual powered developer homogenizer for electrophotographic device

ABSTRACT

A cleaner for removing residual powdered developer from an applicator which applies the developer to a photoconductive electrostatic image-forming member. The cleaner has a flat inclined surface down which the residual developer slides into a reservoir. The homogenizer is mounted above the flat surface perpendicular to the gradient thereof and comprises a rotary shaft carrying a plurality of elliptical plates. The minor axes of the plates perpendicularly intersecting the axis of the shaft and the major axes intersecting the axis of the shaft at an acute angle equal to the arc sine of the ratio of the lengths of the minor axis of the plates and the major axis so that the edges of the plates just touch the flat surface at all rotational positions of the shaft. The plates deflect the residual developer in various directions along the length of the shaft to homogenize the same.

United States Patent [1 1 Nagahara Dec. 16, 1975 RESIDUAL POWEREDDEVELOPER HOMOGENIZER FOR ELECTROPHOTOGRAPHIC DEVICE [75] Inventor:

[73] Assignee: Ricoh Company Ltd., Tokyo, Japan [22] Filed: July 22,1974 [21] Appl. No.: 490,814

Yasumori Nagahara, Tokyo, Japan [30] Foreign Application Priority DataOTHER PUBLICATIONS Cross et al., Magnetic Brush Developer, IBM TechnicalDisclosure Bulletin, Feb. 1967, pp. 1090, 1091, Vol. 9, No. 9.

Primary Examiner-Fred L. Braun Attorney, Agent, or FirmFrank J. Jordan57 5 ABSTRACT A cleaner for removing residual powdered developer from anapplicator which applies the developer to a photoconductiveelectrostatic image-forming member. The cleaner has a flat inclinedsurface down which the residual developer slides into a reservoir. Thehomogenizer is mounted above the flat surface perpendicular to thegradient thereof and comprises a rotary shaft carrying a plurality ofelliptical plates. The minor axes of the plates perpendicularlyintersecting the axis of the shaft and the major axes intersecting theaxis of the shaft at an acute angle equal to the arc sine of the ratioof the lengths of the minor axis of the plates and the major axis sothat the edges of the plates just touch the flat surface at allrotational positions of the shaft. The plates deflect the residualdeveloper in various directions along the length of the shaft to homogenize the same.

8 Claims, 7 Drawing Figures US. Patent Dec-.16; 1975 Sheet 1 of3 v3,926,517

US. Patent Dec. 16, 1975 Sheet 3 of3 3,926,517

- Fig. 6

RESIDUAL POWEREDDEYELOFER HOMOGENIZER FOR ELECTROPHOTOGRAPHIC -DEVICEThe present invention generally relates to an electrophotographic devicehaving means for recycling residual powdered developer, and moreparticularly. to a homogenizer to homogenize the residual developerprior to returningthe. same to a reservoir.

In an electrophotographic device'such as a copying machine to which thepresent invention is directed, an image of a document is projected ontoa photoconductive element to form a latent electrostatic image of thedocument, and the latent image is converted into a visible image by awet or dry development process. In a dry development process, a powdereddeveloper comprising toner and carrier particles is applied by anapplicator onto the photoconductive member. The toner particles aretransferred to a sheet of paper and fixed thereto by means such asthermal fixing, and the carrier particles are returned to a developerreservoir. Light areas of the electrostatic image on the photoconductivemember have no electrostatic charge, whereas dark areas of the imagehave, for example, a positive electrostatic chargeThe toner particlesare dark in color and have a charge opposite to that of the darkportions of the electrostatic image, or in this case a negative charge,so that they will be attracted by and adhere to I the dark image areasof the photoconductive member.

The carrier particles have the same polarity as the dark areas of theelectrostatic image, in this example positive, so that they will attractand carry the toner particles and be repelled by the positive charge ofthe photoconductive member. The charge of the photoconductive member isstronger than that of the carrier particles so that the carrierparticles will be separated from the toner particles when the tonerparticles adhere to the photoconductive member and drop away from thephotoconductive member. The development process is thereby based on theCoulomb attraction between the dark areas of the electrostatic image onthe photoconductive member and the toner particles.

In another known method, the applicator is a rotary magnetic brush andthe carrier particlesare of a magnetic material. As the magnetic brushsweeps the photoconductive member, toner particles are transferred tothe dark areas of the electrostatic image, but the carrier particlesremain adhered to the magnetic brush. Residual toner particles resultingfrom lack of transfer to light areas of the electrostatic image willalso remain adhered to the magnetic brush. This method represents animprovement in that scattering of the residual developer particles islargely prevented. A drawback of this method is that continuousprolonged development will progressively reduce the darkness andcontrast of the developed image since toner particles are consumed andthe carrier particles are capable of attracting only a limited amount oftoner particles.

As an example, if the copy paper onto which the image is transferred isin the form of an elongated strip,

one side of the strip being dark and the other side being light, and themagnetic brush development method is applied along the length of thestrip, the dark areas will continuously consume toner particles whereasthe light areas will not, and the darkness of the developed dark side ofthe strip will progressively decrease. It is clear, however, that tonerparticles are present in the half of the magnetic brush corresponding tothe light side of the image, and if utilized can maintain the dark sideof extreme, it points out the desirability of removing the residualdeveloper particles from the magnetic brush, homogenizing them so thatthe ratio of the concentrations of the toner and carrier particles isuniform, and recycling the developer particles to a reservoir for reuse.

A prior art arrangement to accomplish this object involves a cleaner forthe magnetic brush which comprises an inclined flat plate having itsupper edge engaging with the magnetic brush to scrape residual developerparticles therefrom. Deflecting plates or baffles are arranged above theplate to deflect the residual developer particles sliding down the platein different directions to mix or homogenize the same. Although simplein construction, the practical performance of this arrangement has notbeen satisfactory.

It is therefore an important object of the present invention to providea homogenizer to effectively homogenize residual developer particlesremoved from a magnetic brush of an electrophotographic device such as acopying machine.

The above and other objects, features and advantages of the presentinvention will become more clear from the following detailed descriptiontaken with the accompanying drawings, in which:

FIG. 1 is a plan view of a homogenizer embodying the present invention;

FIG. 2 is a plan view of a plate of the homogenizer shown in FIG. 1;

FIG. 3 is a schematic view of a portion of an electrophotoconductivedevice incorporating the homogenizer shown in FIG. 1;

FIG. 4 is a plan view of the homogenizer shown in FIG. 1 in operativeengagement with a flat surface of a part of the device shown in FIG. 2;

FIG. 5 is a plan view of a modified form of the homogenizer shown inFIG. 1;

FIG. 6 is a view illustrating the profile of a modified form of a shaftof the homogenizer shown in FIG. 1; and

FIG. 7 is a view illustrating a modified form of a plate of thehomogenizer shown in FIG. 1 fixed to a sleeve by which the plate isadapted to be mounted on the shaft shown in FIG. 6.

Referring now to FIG. 1, a homogenizer 10 embodying the presentinvention comprises a shaft 12. Elliptical plates 14 are mounted on theshaft 12 by means of sleeves 16 respectively. Referring also to FIG. 2,the major axis of each plate l4'has a length a and the minor axis has alength b. The minor axis of each plate 14 perpendicularly intersects theaxis of the shaft 12, and the major axis of each plate 14 intersects theaxis of the shaftl2 at an acute angle 0. The relationship is such that ba (sin 0). 0 arc sin (b/a), and is shown in the drawings as 45. 5

Referring now to FIG. 3, a copying machine 18 includes a casing 20, thebottom portion of which defines a reservoir 22 containing powdereddeveloper in the form of carrier and toner particles. Fresh developer isfed into the reservoir 22 through a hopper 24. A photoconductive drum 26is provided on which an electrostatic image of a document being copiesis formed by an optical system (not shown), and which rotatescounterclockwise. An applicator in the form of a rotary drum 28 having abrush (not shown) provided on its circumference has its lower portionimmersed in the developer in the reservoir 22 and rotatescounterclockwise. Although not shown, the brush of the drum 28 isarranged to slidably contact the surface of the drum 26 as the drums 26and 28 are simultaneously rotated. Magnets 28a, 28b, 28c and 28d arefixedly mounted within the drum 28 adjacent to the inner surface thereofnear the contact area of the drums 26 and 28.

The shaft 12 of the homogenizer 10 is rotatably supported within thecasing 20 above a cleaner 30 in the form of a flat plate. The cleaner 30is rotatably supported by the shaft 12 by means of hangers 32, one ofwhich is shown. The cleaner 30 is inclined as shown, and the upper edgeof the cleaner 30 engages with the brush of the drum 28 to removeresidual developer therefrom. The residual developer slides down theflat upper surface of the cleaner 30, passes through the homogenizer land drops down into the reservoir 22 for recycling. Toner and/or carrierparticles may be continuously or periodically introduced into the hopper24 at a fixed concentration ratio of carrier/toner particles. A feedrotor 34 is also provided to move the developer particles into the areaof the reservoir 22 under the drum 28.

In operation, the optical system projects an image of the document ontothe drum 26 to form a latent electrostatic image. The brush of the drum28 picks up developer from the reservoir 22 due to the effect of themagnets 28a, 28b, 28c and 28d and transfers the same to the drum 26 todevelop the latent image. Toner particles are attracted by and adhere todark areas of the I the homogenizer l0 and drop down into the reservoir22. The residual developer particles may be easily removed from thebrush of the drum 28 because there are no magnets arranged inside thedrum 28 near the cleaner 30, and the magnetic attraction of the drum 28and brush for the developer particles near the cleaner 30 is very low.

The purpose of the homogenizer 10 is to throughly mix or, homogenize theresidual developer particles passing therethrough so that the ratio ofthe concentration of carrier particles to toner particles will be thesame for particles emerging from all points of the homogenizer 10 toprovide a homogenious powdered del veloper for recycling.

The detailed operation of the homogenizer 10 will now be described withreference to FIG. 4. As shown,

the bottom edges of the plates 14 are closely adjacent to the upper flatsurface of the cleaner 30; either the plates 14 just touch the cleaner30 or the clearance 1 therebetween is very small. The residual developerparticles move through the homogenizer perpendicular to the plane ofFIG. 4, or down the gradient of the flat surface of the cleaner 30. Aswill be understood by one skilled in the art, due to the relationship!)arc sin(- b/a), the edges of the plates 14 will just touch the surfaceof the cleaner 30 at all rotational positions of the homogenize theresidual developer as the same movesshaft 12. If desired, theprojections of the major axes of the plates l4 on aplane perpendicularto the axis of the shaft 12 may coincide, as shown in FIG. 5, so thatthe orientation of all of the plates 14 is the same. In a preferred formof the present invention, however, the projections of the major axes ofthe plates 14 on a plane perpendicular to the axis of the shaft 12 donot coincide, but are equiangularly spaced about the axis of the shaft12. For example, as shown in FIG. 4, if the projection of the major axisof the leftmost plate 14 as shown is oriented vertically in a planeperpendicular to the shaft 12, the projection of the major axis of thesecond plate 14 from the left will appear as rotated by 90. Theprojections of the major axes of the third plate 14 from the left andthe rightmost plate 14 will appear in said plane as rotated by l and 270respectively from the vertical position of the first plate 14, and willbe sy'rnmetrical to the first and second plates 14 from the leftrespectively.

In the embodiment shown in FIG. 4, the homogenizer 10 is freelyrotatably mounted within the casing 20 and will be rotated by thedeveloper particles passing therethrough. Since the plates 14 arearranged at, angles to each other along the length of the shaft 12, theplates 14 will deflect the developer particles in different directionsas the particles pass through the homogenizer l0, and particlesdeflected by one plate 14 will mix with particles deflected in anintersecting direction by another plate 14 along the length of the shaft12 so that the residual developer particles will be effectively andefficiently homogenized as they slide down the upper surface of thecleaner 30 and drop into the reservoir 20.

In FIG. 5 the plates 14 are shown as all having the same orientation asmentioned above, and the shaft 12 is rotatably driven from drive means(not shown) through a drive shaft 40, pulley 42 and belt 44.

FIGS. 6 and 7 illustrate an accurate, simple and inexpensive method ofassembling and aligning plates 14 on a shaft 12'. The shaft 12 is shownas having a hexagonal profile, and the bore of a sleeve 16 is alsohexagonal and has the same size and profile as the shaft 12'. Each plate14 may be assembled onto the shaft 12' simply by sliding the attachedsleeve 16 onto the shaft 12'. In this example, the angular spacingbetween the major axes of two adjacent plates 14' may be accuratelyprovided as 60, 240, 300 or 360 as desired. Naturally, the profile ofthe shaft 12' may be in the form of a polygon having any number of sidesto provide any desired equiangular relationship between the major axesof the plates 14'. Also, if the round shaft 12 is utilized, the plates14 may be welded or otherwise secured thereto so that the relationshipsbetween the major axes of the various plates 14 is not equiangular, andmay be random if desired.

What is claimed is:

1. In an electrophotographic device having a photoconductive memberadapted to produce an electrostatic image of a document, an applicatorfor applying powdered developer to the photoconductive member to developthe image and a cleaner for removing resid-" ual developer from theapplicator, the cleaner having an inclined flat surface down whichresidual developer wherein the improvement comprises a homogenizer todown the flat surface, said homogenizer comprising:

a shaft rotatably mounted above and in a plane parallel to the flatsurface the axis of said shaft being substantially transverse to thedirection of movement of the residual developer; and a plurality ofsubstantially elliptical plates mounted for rotation with said shaft,the minor axes of said plates perpendicularly intersecting the axis ofsaid shaft and the major axes of said plates intersecting the axis ofsaid shaft at an acute angle, the edges of said plates being closelyadjacent to the flat surface at all rotational positions of said shaft;whereby residual developer moving down the flat surface is deflected bysaid plates and thereby homogenized. 2. A homogenizer according to claim1, in which projections of the major axes of said plates on a planeperpendicular to the axis of said shaft are equiangularly spaced aboutthe axis of said shaft.

3. A homogenizer according to claim 1, in which said acute angle betweenthe major axes of said plates and the axis of said shaft is equal to thearc sine of the ratio 6 of the lengths of the minor axis of said platesto the major axis of said plates.

4. A homogenizer according to claim 1, in which the electrophotographicdevice has drive means, and said shaft is rotatably driven by the drivemeans.

5. A homogenizer according to claim 1, which is rotated by the movingresidual developer.

6. A homogenizer according to claim 1, in which the electrophotographicdevice has a reservoir for the developer, the applicator being operativeto pick up developer from the reservoir, and in which said homogenizeris arranged to recycle the residual developer into the reservoir.

7. A homogenizer according to claim 1, in which said shaft has apolygonal profile, and which further comprises sleeves to mount theplates respectively on said shaft, the bores of said sleeves havingsubstantially the same profile as said shaft.

8. A homogenizer according to claim 1, in which projections of the majoraxes of said plates on a plane perpendicular to the axis of said shaftcoincide.

1. In an electrophotographic device having a photoconductive memberadapted to produce an electrostatic image of a document, an applicatorfor applying powdered developer to the photoconductive member to developthe image and a cleaner for removing residual developer from theapplicator, the cleaner having an inclined flat surface down whichresidual developer moves after being removed from the applicator,wherein the improvement comprises a homogenizer to homogenize theresidual developer as the same moves down the flat surface, saidhomogenizer comprising: a shaft rotatably mounted above and in a planeparallel to the flat surface the axis of said shaft being substantiallytransverse to the direction of movement of the residual developer; and aplurality of substantially elliptical plates mounted for rotation withsaid shaft, the minor axes of said plates perpendicularly intersectingthe axis of said shaft and the major aXes of said plates intersectingthe axis of said shaft at an acute angle, the edges of said plates beingclosely adjacent to the flat surface at all rotational positions of saidshaft; whereby residual developer moving down the flat surface isdeflected by said plates and thereby homogenized.
 2. A homogenizeraccording to claim 1, in which projections of the major axes of saidplates on a plane perpendicular to the axis of said shaft areequiangularly spaced about the axis of said shaft.
 3. A homogenizeraccording to claim 1, in which said acute angle between the major axesof said plates and the axis of said shaft is equal to the arc sine ofthe ratio of the lengths of the minor axis of said plates to the majoraxis of said plates.
 4. A homogenizer according to claim 1, in which theelectrophotographic device has drive means, and said shaft is rotatablydriven by the drive means.
 5. A homogenizer according to claim 1, whichis rotated by the moving residual developer.
 6. A homogenizer accordingto claim 1, in which the electrophotographic device has a reservoir forthe developer, the applicator being operative to pick up developer fromthe reservoir, and in which said homogenizer is arranged to recycle theresidual developer into the reservoir.
 7. A homogenizer according toclaim 1, in which said shaft has a polygonal profile, and which furthercomprises sleeves to mount the plates respectively on said shaft, thebores of said sleeves having substantially the same profile as saidshaft.
 8. A homogenizer according to claim 1, in which projections ofthe major axes of said plates on a plane perpendicular to the axis ofsaid shaft coincide.